Notwithstanding the provisions of §§ 60.2-500 through 60.2-536, if § 3303 of the Internal Revenue Code is amended so as to allow an additional credit under § 3302 (b) of the Internal Revenue Code to employers not otherwise eligible for a reduced rate by reason of the lapse of insufficient time since first becoming subject to this title, the Commission, by a regulation promulgated under § 60.2-111, shall fix and determine the tax rate of all such employers at such reduced rate as shall then be permissible under such federal amendment.